For me, the best looking would be the Leica III series, original Nikon F, OM1, SL66, early Bronicas (Z, D, S), and any Ebony.

I was hoping someone would reply and say these were ugly. Because beauty is in the eye of the beholder. A camera is a tool. It is like saying which is more beautiful a hammer or a polished gold plated hammer. Who cares.